k100RS Cold Knock

[bprigge]

Hello all, again

I have a 91 K100RS that has a knock when cold at rpms below about 1100.
The knock goes away before the temp gauge gets out of the blue, maybe after two to three minutes of running. In fact with carefull use of the enrichner lever you will never hear the knock. I've put 2k+ miles on the bike in the past month and the sound hasn't changed at all.

Having a heightened sense of 'searchness' i've spent a couple of days doing research on this site and all over the internet and have located information that points to the hydraulic cam chain tensioner as the culprit. The tensioner apparently has a ratcheting mechanism in it that holds a setting after oil pressure drives the piston out. The racheting provision has been known to fail according to an article on Flyingbrick.de, causing a cold knock (the article said 'bang') that goes away when the engine is warmed up.

Anyway, has anyone here had any experience with this? I would like to take the cam chain cover off this weekend and examine the tensioner but my service manual hasn't arrived yet and I don't know what all i'm getting into in regards to coolant, sensors, etc. The motor has 55k miles on it and has been run on Amsoil 20w50 it's entire life. I don't know how long the knock has been there as I am the 2nd owner. Also, the bike has a Staintune exhaust system. I am mentioning that because the knock sometimes sounds like it's comming from the muffler.

The best way I can describe the knock (to an experienced mechanic) is that it sounds like what you hear if you pull a plug wire off of a 4 cylinder motor. I've considered that it might be missing on one cylinder at start up and haven't completley abondon that idea. It does run very smoothly on start up though.
Also, I can feel the knock in the grips when it is at it's loudest. That would be at a slow idle right after a cold start up.
Any advice or experience appreciated. thanks, Bruce

 

[pfetter]

K100 Cold Knock

I have a 86 K100RT, that I have only put a few miles on since I purchased it. It has 130000 miles on it, but I also notice that when I start the bike it knocks or rattles for a couple minutes. I was assuming that it was due to parts waiting for the oil to get to them but I sure would be interested in knowing what you find out it you take yours apart.
Paul

 

[bprigge]

Paul,

Check out this link. Look about 4 paragraphs down under the comments about cam chains.

http://www.flyingbrick.de/GB/faq.html

Even Gail will have to admit this indicates serious rersearch was done. We're talking a German language Beemer site no less.


Following is a cut and paste from flyingbrick.de, the menu pick called 'used bikes'. (Might be 'used motorcycles')


"
Leakages may occur at the combined oil/water pump. A service kit is available, the complete repair can be done for the price of 200 Euro, according to information given by the forum guests. An oil leakage between engine and gearbox or at the shaft drive housing is more expensive, and the final drive may be destroyed due to lack of lubrication. Front fork tubes of the early K100 are prone to leak, the new fork seals aren??t expensive. More expensive are repairs to the driveshaft and clutch connection. This consists of two gears that are connected. Defective engines make a knocking noise. Banging noises that reduce with increased engine temperatures are caused by a defective hydraulic chain tensioner. This tensioner needs to be replaced with the guide rail. Even for this kind of work, all you need to do is remove the engine cover! "

 

[jdiaz]

I think its the riveted anti-vibe damper on the layshaft.

 

[bprigge]

Jon,

Last night I was all over the motor with a stethoscope and it sounded slightly louder at the right rear of the motor, or it least I think it did. I also put the bike in 2nd gear and let the clutch partially out with the brakes on hard to load the motor. This didn't seem to change the noise.
Are the anti vibe damper rivets a hazard to my health, or the bikes health?
Seems like I read somewhere that the 4 valve motors had more rivets in them then the 2 valve motor. Bruce

 

[jdiaz]

I don't know if loosening of the anti-vibe rivets are problematic long-term. I don't think they are, but others surely have more long-term experience with a K four than me.

It isn't worth taking the engine apart to fix it, because you can get a used low-mileage engine for less money than that single part will cost. So ride the current bike until it dies.

 

[bprigge]

Thanks Jon, looks like more research will be necessary here. Bruce

 

[deilenberger]

It more than likely is the anti-rattle assembly where the crankshaft and output shaft mate. When the engine is cold - it's usually running just a bit rougher - and that will cause components to make noise.

If it goes away after a few moments - I wouldn't worry about it. Put your earplugs in before you start the engine and you'll never know it's doing it.

 

[bprigge]

deilenberger and jdiaz,

Wouldn't the anti-vibe / anti-rattle device cease to make noise when I take up the slack in the drive line components by letting the clutch out partially with the brakes on and engine running? It would be good to see a picture of how this thing is put toghether, or better yet see the real thing. Bruce

 

[bprigge]

Here is a cut and paste from flyingbrick.de, the 'Used Motorcycle' section.




"
Leakages may occur at the combined oil/water pump. A service kit is available, the complete repair can be done for the price of 200 Euro, according to information given by the forum guests. An oil leakage between engine and gearbox or at the shaft drive housing is more expensive, and the final drive may be destroyed due to lack of lubrication. Front fork tubes of the early K100 are prone to leak, the new fork seals aren??t expensive. More expensive are repairs to the driveshaft and clutch connection. This consists of two gears that are connected. Defective engines make a knocking noise. Banging noises that reduce with increased engine temperatures are caused by a defective hydraulic chain tensioner. This tensioner needs to be replaced with the guide rail. Even for this kind of work, all you need to do is remove the engine cover! "

 

[deilenberger]

deilenberger and jdiaz,

Wouldn't the anti-vibe / anti-rattle device cease to make noise when I take up the slack in the drive line components by letting the clutch out partially with the brakes on and engine running? It would be good to see a picture of how this thing is put toghether, or better yet see the real thing. Bruce

Not really.. the best description of it was in Mick Walkers book on K bikes - he also covered the various engineering changes BMW made to it to try to make it actually work.

One other possibility - the alternator drive rubbers (goobers AKA MonkeyNutz) may have hardened up. These are about a 5 year replacement item. If they really go bad - the vanes on the cup and drive part can break and cause all sorts of interesting noises. That also is in the same general area - but willing to bet what you're hearing is the anti-rattle gear rattling around.

 

[deilenberger]

Defective engines make a knocking noise. Banging noises that reduce with increased engine temperatures are caused by a defective hydraulic chain tensioner.[/COLOR] This tensioner needs to be replaced with the guide rail. Even for this kind of work, all you need to do is remove the engine cover! "

I guess this is possible - but the noise would be from up front where the cam chain is.. and I've never heard of one of these actually failing. At one time BMW had a replacement interval for the plastic tensioning guide - but no one ever found one that wore out so that went by the wayside.

Could be - but betting it isn't the cam chain.

 

[deilenberger]

I don't know if loosening of the anti-vibe rivets are problematic long-term. I don't think they are, but others surely have more long-term experience with a K four than me.

The rivets are actually what couple the gear to the shaft - the driving gear on the output shaft. The K100 has a rubber damper in the output shaft, and the driving gear is on the outside of the damper housing, riveted to it. When the rivets fail the bike looses forward motion. No big drama - it just doesn't go anymore. Engine runs, but nothing comes out of it.

The 2 valve K used 6 rivets. The 4 valve used 12. Supposedly you can see these rivets by taking off the crankcase cover and looking way down and to the back of the engine guts. I've never tried so that's 2nd hand info. Most people have some warning of impending failure by finding a rivet head in their drain oil. That's a clue it's time to consider fixing it.

It isn't worth taking the engine apart to fix it, because you can get a used low-mileage engine for less money than that single part will cost. So ride the current bike until it dies.

Absolutely.. the engines are so reliable they are sold as doorstops. I had one with 1,000 miles on it as a doorstop for a long time. Sold it to a friend - it's his doorstop now. If anyone wants an almost brand new '85 K100 engine (the FAST year) - I'm sure he'd sell it for less than the output shaft costs.

 

[bprigge]

Thanks Don!!

My experience with bike motor noises has been that they can be extremely hard to find. I think I'm going to take the timing cover off and inspect the hydraulic tensioner after my service manual arrives.

I tried something this morning just for the sake of science that I hadn't tried before. I started the motor from completely cold with no choke. It fired right up and idled at 700 or so. It took the motor maybe 10 or 15 seconds to start making the noise. My theory is that the cam chain is tight do too the hydraulic tensioner
having put good tension on it before the motor was last shut down. The ratched mechanism, being the flacky part, then ceases to hold and the natural forces of the cam chain push the tensioner back partway, letting one or both cams spring back during certain parts of their rotation, until the tensioner once again takes up the slack. I can't explain why this would be thermal unless clearances in the ratchet mechanism change in an unfavorable way when cold. Looks like the only way this can be eliminated as a possibility is to examine or change the hydraulic tensioner. This would be a lot easier to do then pull the motor down far enough to examine the drive anti-rattle mechanism. That would be a good project for a Minnesota winter. If its not the tensioner and as long as the anti-rattle device isn't going to lock up my driveline at 80 mph I guess i'll just live with it this summer. Bruce

 

[bprigge]

Here's an interesting developement. I did a cylinder leak down test today and found number 4 cylinder to be at a 40 percent leak rate. The other three are close to a 0 percent leak rate, mayby two percent or so. I can hear the pressure bleeding off through the muffler making me think I got a burnt exhaust valve in #4. Now i'm pretty certain that the motor is cranking up cold on three cylinders at idle and i'm hearing what that sounds like. I think it's going to have to stay that way til late fall. The bike gets 48 to 54 mpg, is quiet at idle after a couple of minutes of run time and makes what feels like normal power. The motor has used a couple of ounces of oil in the 2500 miles i've put on it. I checked the valve lash on #4 hoping to find an exhaust valve with little or no lash but all 4 valves were within .001 of specs. Bruce